I don't soak it for days. I usually soak it just overnight, and sometimes just for a few hours. I usually get about 30 - 40% of it sinking to the bottom. I realize this is a very imperfect method, as if you don't wait long enough, non sinks, and if you wait too long, all of it sinks. There's a happy medium in there.
Also, I really like Tamlin's advice to wring it out and transfer to another bucket. This really accomplishes the same thing, by squeezing out the sludge.